Since the divestiture of the American Telephone and Telegraph Company in 1984, the Regional Bell Holding Companies (RBHCs) have focused their efforts on cutting operating costs, upgrading their networks, providing new high speed services, and interconnecting their networks to long-distance companies and international carriers. One of the new services under review for offering by the RBHCs is Video-On-Demand (VOD) service. VOD service permits customers to order from a defined library of movies and other programs at any time--thus "on-demand" availability.
In order to provide a sufficient number of video circuits to meet expected demand, network designers have typically relied upon existing methodology and, in particular, the Erlang-B method for predicting the required network size for a certain quality of service for blocking, i.e., the probability that subscriber demand will exceed available circuits. The Erlang-B method has historically been used for sizing telephony networks and is based on an M/M/C/C queuing system. In particular, given C circuits in the networks, the blocking probability, P.sub.C.sup.Erlang, is given by: ##EQU2## .lambda. is the average arrival rate, and .beta. is the average holding time.
As those skilled in the art will recognize, the Erlang-B method assumes poisson arrivals (M) and exponential service time distribution (M), i.e., the holding time of telephone calls being exponentially distributed. These assumptions, however, have been found not to be valid in video delivery networks where call holding time is generally constant and relatively long. Because of the special computational methods required to determine the factorials of large numbers--as required by the Erlang-B method--the method has similarly been found to be exceedingly difficult and time consuming to implement in practice. For these reasons, network designers have turned their attention toward the development of alternative methods and systems for sizing interactive video delivery systems which are accurate and easy to implement.